1. Field of the Invention
This invention relates to an expansion anchor capable of being expanded in a fitting hole bored in a foundation of concrete, stone, porcelain tile or other rigid materials so as to be secured in a non-removable state.
2. Description of the Prior Art
There has been generally known an expansion anchor of this type which comprises a cylindrical anchor body 1 having an axial hole 1a, longitudinal slits 1b and a contracted portion 1c, and a pin member 2 to be thrust into the axial hole 1a, as shown in FIG. 1. Upon inserting the anchor body 1 into a fitting hole H bored in a rigid material B such as concrete, the pin member 2 is forced into the axial hole 1a of the anchor body 1, causing the anchor body 1 to expand and come into frictional contact with the inner wall surface of the rigid material B defining the fitting hole H in a non-removable state.
There has been another type of the expansion anchor comprising a cylindrical anchor body 3 having an axial hole 3a and longitudinal slits 3b, and a wedge plug 5 connected to a threaded bolt 4, as shown in FIG. 2. By turning the threaded bolt 4, the wedge plug 5 is drawn into the axial hole 3a of the anchor body 3, causing to expand and be secured the anchor body 3 in the fitting hole.
In any conventional expansion anchor, only one part of the outer peripheral surface of the cylindrical anchor body is expanded by the pin member or wedge plug forced into the anchor body. That is, the anchor body is partially expanded to be fastened to the rigid material. In substance, only the leading edge portion of the anchor body is expanded and comes into partial engagement with the inner wall surface defining the fitting hole. Thus, the engaging strength brought about by the expansion anchor is not sufficient for uniting the anchor body with the rigid material.
Hence, the conventional expansion anchor in the expanded state in the fitting hole of the rigid material cannot be steadily secured when the fitting hole is not accurately formed or the rigid material is frail, or will possibly come out easily from the fitting hole due to various external causes such as vibrations.
The conventional expansion anchor of this type is generally provided on the outer surface of the anchor body 1 or 3 with checking steps 1d or 3d to increase the frictionally engaging strength relative to the rigid material, as illustrated in FIG. 1 and FIG. 2. However, the anchor is nontheless not reliably secured to the rigid material, because the anchor body is partly engaged at the leading edge portion thereof with the rigid material, all the same, as described above.